1. Field of the Invention
The present invention relates to the field of semiconductor substrate processing equipment More particularly, the present invention relates to an improved lid assembly for a process chamber that allows the lid to "float" above the chamber so that the lid may be properly centered on the chamber.
2. Background of the Related Art
In the fabrication of integrated circuits, equipment has been developed to automate substrate processing by performing several sequences of processing steps without removing the substrate from a vacuum environment, thereby reducing transfer times and contamination of substrates. Such a system has been disclosed for example by Maydan et al., U.S. Pat. No. 4,951,601, in which a plurality of processing chambers are connected to a transfer chamber. A robot in a central transfer chamber passes substrates through slit valves in the various connected processing chambers and retrieves them after processing in the chambers is complete.
The processing steps carried out in the vacuum chambers typically require the deposition or etching of multiple metal, dielectric and semiconductor film layers on the surface of a substrate. Examples of such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), and etching processes. Although the present application primarily discusses CVD processes, the present invention is equally applicable to other processes as well.
Process chambers are employed to deposit thin films on semiconductor substrates. Typically, in a CVD process, a precursor gas is charged into a process chamber through a gas manifold plate situated above the substrate. The precursor gas reacts on the heated substrate surface to deposit a thin layer thereon.
To increase manufacturing efficiency and device capability, the thin films deposited on the substrates must be of uniform thickness across the substrate so that all of the devices on the substrate are uniform. Additionally, increased throughput requires that as much of the upper surface area of each of the substrates be utilized while preventing edge and backside deposition on the substrate. Material deposited on the beveled edge and the relatively rough backside of the substrate has a tendency to flake off and create particles which are harmful to the processing equipment as well as the substrates and devices being processed. One way to help ensure that the films are uniform and that the required portions of the substrate are properly shielded is to utilize tight tolerances in aligning the various components of the system. For example, in a typical CVD process chamber the components to be aligned include the substrate and the shielding shadow ring positioned over the substrate which are aligned relative to the gas manifold that is typically positioned in the lid of the process chamber.
The lids for the process chambers are connected to the chamber by a hinge and may be selectively opened during down times to perform maintenance on the process chambers. Therefore, the interface between the lid and the process chamber must include a seal to maintain the vacuum in the process chamber and to prevent the gases used in the process from leaking into the environment. Further, when the lid is closed, it must be properly positioned on the process chamber to align the chamber components in the lid (e.g., a gas manifold in a CVD process) to the other process chamber components, such as the support member and a substrate positioned thereon.
One prior art process chamber having a lid that may be selectively opened is shown in FIG. 1. As shown in the figure, the lid is connected to the process chamber by a hinge at the back of the lid. A pneumatic cylinder attached to the process chamber and to the lid at a point intermediate the front and the back of the lid provides support and assists in opening and closing the lid. The hinges include an arm attached to the lid at the top end of the arm and attached to a hinge mount at the bottom end of the arm. The hinge mount has a circular pin extending horizontally therefrom that extends through an elongated slot (i.e., oval-shaped holes) in the arm. Thus, as the lid is opened and, thereby, rotated about the hinge, the arm is free to move longitudinally relative to the pin because of the slot. Likewise, the lid has a limited ability to "float," or move, above the process chamber as the lid is closed and before being secured to the chamber. In this way, as the lid is closed, the back of the lid may be lifted, so that the lid can be positioned in parallel alignment with the process chamber before closing, and the lid is then lowered over the opening. Therefore, the position of the lid on the chamber is adjustable to permit proper placement for alignment and for proper sealing.
However, in the quest for greater throughput, the size of the substrates has become larger which, in turn, requires larger process chambers to accommodate the substrates. The larger chambers require larger lids which are heavier and more difficult to open and close. Consequently, the heavier lids of the larger chambers are more difficult to properly align as the lid is closed because the heavier lid is more difficult to lift and manipulate than the smaller lids of the previous designs. Therefore, with a heavier lid it is more difficult to obtain the needed alignment of the lid relative to the chamber and, thus, to obtain the required seal.
Therefore, there is a need to provide an improved lid that is more easily opened and closed and that facilitates proper placement of the lid on the chamber.